This invention relates to highly cross-linked poly(benzimidazoquinazolines) and to the prepolymers and process for making them.
Poly(benzimidazoquinazolines) have previously been made by several methods using various reactants. One method consists of synthesizing the poly(benzimidazoquinazoline) in polyphosphoric acid from bisbenzoxazinones and tetramines or from 2,2'-(o-aminoaryl)bisbenzimadazoles and aromatic acid chlorides [N. Yoda and M. Kurihara, Macromol. Rev. 5D, 178 (1971)]. A major disadvantage of this method is that the resulting linear poly(benzimidazoquinazolines) are infusible and unprocessable. That is, they cannot be used, for example, to impregnate fibers to produce laminates or as molding compounds to produce molded articles. A second method of producing poly(benzimidazoquinazolines) comprises the solution condensation of 2,2'-(o-aminoaryl)bisbenzimidazoles with aromatic di- or tri-acid chlorides followed by ring closure under vacuum at elevated temperatures as described in U.S. Pat. No. 3,503,929, issued Mar. 31, 1970. A difficulty with this method is that, although the intermediate polyamidobenzimidazole polymer is processable, it must be purified by isolation from the condensation solvent and redissolved prior to use. A third method is described in the latter patent and comprises the melt condensation of a tetramine and a diphenyl ester of N,N'-di(o-carboxy phenyl) dicarboxylic acid amide followed by solid-state polymerization. A limitation of both of the methods described in U.S. Pat. No. 3,503,929 is that the disclosed polymers are essentially linear and thus do not exhibit the more desirable characteristics of highly cross-linked systems.